1. Field of the Invention
This invention relates to a lighting device utilizing an LED device, an image pickup apparatus equipped with the lighting device, and a portable terminal unit equipped with the image pickup apparatus.
2. Description of the Related Art
Some of the latest portable telephones are integrally equipped with a camera. However, the camera mounted on such portable telephones is not suited for use in taking a photograph of a clear image especially when a subject is dark. Further, the image photographed by the camera is poor in clearness in red, and there is a problem, when the subject photographed is a human figure, that the picture quality of yellowish-pink becomes poor. The quality of these characteristics depends largely on the brightness of flashlight emitted from the flashing device mounted on the portable telephones and on the performances such as color rendering properties, etc.
The flashing device to be mounted on the latest portable telephones can be generally classified into two types. One of them is based on a system where a plurality of white LED devices, each formed of a combination of a blue light emitting diode and a phosphor, are employed. In the case of this system, although it is possible to secure brightness from an LED device which is higher than a predetermined level, there are problems that the color rendering properties thereof are poor and the image photographed is poor in clearness. Especially, as described above, when a human figure is photographed, the yellowish-pink thereof becomes poor.
The other type is based on a system where white color is obtained through a combination of red (R)-, green(G)- and blue(B)-emitting diodes. In the case of this system, although it is possible to realize a flash having excellent color rendering properties, there are problems that since it is required to concurrently drive a plurality of light emitting diode chips differing in characteristics from each other, the control circuit thereof becomes complicated, thus making it difficult to realize the miniaturization of the device and to reduce the manufacturing cost thereof.
In addition to the aforementioned systems, there have been also proposed various kinds of systems such as a system wherein an ultraviolet light emitting diode chip and a red light emitting diode chip are combined (see for example, JP Laid-open Patent Publication (Kokai) No. 2004-71807), etc. However, even with these systems, it is difficult to overcome both problems of aforementioned brightness and the driving of light emitting diode chips.
There is also known a method wherein a white LED is prepared through a combination of ultraviolet-, near-ultraviolet- or bluish violet-emitting diode and a phosphor, and the resultant white LED is used for preparing a flashing device. However, since it is impossible to sufficiently excite a red phosphor by making use of the light of wavelength which these light emitting diodes emit, there is also a problem that the intensity of the red component in the spectrum will be weak.